Modified polymers

ABSTRACT

A modified polymer is described comprising a thermoplastic polymer composition comprising a graft copolymer between (1) a preformed thermoplastic polymer and (2) a monomer composition comprising (a) at least one polymerisable monomer containing a polymerisable group and at least one functional polymer-modifying group and (b) at least one comonomer containing at least two polymerisable groups, said copolymer being substantially free of unbound monomer. Such polymers can be produced by reacting together, in a melt and in the presence of free radicals whilst applying shear to the melt, the preformed thermoplastic polymer to be modified, the polymerisable monomer, and the comonomer, thereby to graft said monomer to said preformed polymer leaving substantially no unbound monomer, the reaction being continued for a period of time sufficient to produce a graft copolymer that is thermoplastic and can be blended with an unmodified polymer. A free radical generator can be added, if desired.

This invention relates to the modification of thermoplastic polymers togive thermoplastic polymer adducts which contain residues of modifiermolecules bound to the polymeric substrate.

Thermoplastic polymers usually comprise essentially linear molecules ormolecules with only relatively short side chains. They do not, as ageneral rule, contain significant amounts of cross-linking, sincecross-linking tends to increase the rigidity of the polymer throughformation of a tangled matrix of cross-linked polymer chains. Includewithin this class of polymers are vinyl polymers and copolymers andsubstantially linear condensation polymers. Such vinyl polymers andcopolymers include, for example, polyolefins, such as polyethylene andpolypropylene, polyvinyl chloride, polystyrene, ethylene-propylene co-and ter-polymers, polyacrylates, polymethacrylates, polyacrylonitrile,and acrylonitrile-butadiene-styrene terpolymers, to name but a few.Examples of thermoplastic condensation polymers include polyamides,polyesters, and linear and substantially linear polyurethanes.

There is increasing concern about the migration and loss of additivesfrom thermoplastic polymers. This concern arises from several causes.Firstly, if the additives (for example, antioxidants, stabilisers,plasticisers, antistatic agents, photosensitisers and the like) are lostfrom the polymer by volatilisation or leaching, then they no longerfulfil their intended purpose. Secondly, when additives are leached intothe contacting medium for example by foodstuffs or by other extractantsthat are subsequently ingested, then they may cause toxicity in the hostenvironment. Thirdly, when polymers are used in medical applications,for example in surgical goods, prostheses or body implants, it isessential that no migration of additives occurs since although polymersare normally biologically inert, low molecular weight additives aregenerally not so and because they are readily leached into thebiosystem, they cause toxicity problems. Traditionally, additives, andparticularly stabilisers, have been relatively low molecular weightmaterials of high volatility and with marginal compatibility with thebase polymer.

Recently, it has been proposed to overcome the problem of migration andloss of antioxidants and stabilisers by copolymerising antioxidantscontaining vinyl groups with a major proportion of conventional monomersto give polymers containing the appropriate antioxidant in polymerisedform at the concentration required for use during service. This is anexpensive procedure and to overcome this it has been proposed, in, forexample, U.S. Pat. No. 4,354,007 to Scott (hereinafter referred to as"the '007 Patent"), that a wide variety of antioxidants and stabilisersmay be reacted with preformed polymers in the presence of free radicalsto provide a stabilised polymer directly or to make an intermediate,highly concentrated polymer-bound adduct which may be blended withfurther amounts of a suitable compatible base polymer to give anantioxidant modified polymer suitable for a wide variety of end useapplications. The technique is particularly applicable to rubbers inlatex form.

The '007 patent describes a wide variety of antioxidant and stabilisermolecules including compounds selected from categories which includechain-breaking or peroxide-decomposing antioxidants, ultravioletscreening agents, triplet quenchers and metal deactivators. In terms ofa limitation on the scope of the stabiliser compounds that may be used,perhaps the most significant structural limitation is that it should becapable of being activated by a free radical in the polymer (see col. 1,lines 40-50). In this regard, however, it has been found with regard tothe unsaturated or vinyl group-containing stabiliser compounds describedin the '007 patent and also as to similar stabiliser compounds whichhave been suggested by others for grafting to pre-formed polymers in thepresence of free radicals, that frequently the reactivity of thestabiliser molecules containing polymerisable groups may be such thatthe stabiliser may tend to homopolymerise with itself to form a polymeror oligomer. Such an oligomer may, of course, have increased molecularweight as compared to the individual stabiliser molecule and thisincreased weight may inhibit undesired volatilisation, and/or migrationof the stabiliser in the polymer composition.

Unfortunately, however, homopolymerisation or oligomerisation of theadditives generally results in decreased activity of the additive in thepolymer system. Thus antioxidants and stabilisers generally show overalllower stabilisation activity compared with a polymer system containing acomparable amount of grafted antioxidant or stabiliser molecules, and inaddition, the lower molecular weight polymers formed byhomopolymerisation of the additive are readily extracted from thepolymer by extracting media.

In U.S. Pat. No. 4,743,657 to Rekers and Scott a method is proposed forpreparing a polymer bound stabiliser which comprises reacting astabiliser precursor molecule containing a reactive double bond which isnot readily homopolymerisable with a pre-formed polymer in the presenceof a free radical.

In co-pending European Patent Application No. 88302389.7 to Scott,Al-Malaika and Ibrahim filed 18th Mar. 1988 (which was published on 5thOct. 1988 as EP-A-0285293) there is described a process for preparing abound antioxidant polymer concentrate for use as a masterbatch forblending with unmodified polymers which comprises grafting one or moreacrylic or alkylacrylic esters or amides containing a hindered aminegroup onto the polymer in the presence of a radical generator at atemperature of 100° C. to 350° C., the molar ratio of said radicalgenerator to said ester or amide being from 0.001:1 to 1:1, the reactionbeing typically carried out in a melt and being continued for a timesuch that the melt viscosity of the polymer which increases initiallyduring the reaction has reduced to a level which permits the concentrateto be homogeneously blended subsequently into an unstabilised polymer.

EP-A-0247861 to Bromine Compounds Ltd. describes flame retardant polymercompositions possessing non-linear structural configurations which areproduced by reacting a preformed backbone polymer selected frompolyolefins or styrenic polymers or copolymers thereof with atribromophenoxy- or pentabromophenoxy-ethyl-ester of acrylic- ormethacrylic acid. It is stated at page 4 line 49 et seq.:

"The compositions according to the present invention may be prepared byany of the conventional technique of free radical grafting orcrosslinking processes used, e.g. mechanical, thermal radiation induced,or chemically induced and by any of the technologies commonly used suchas bulk, solution, emulsion suspension polymerization or reactive meltprocessing.

Whereas the system according to the invention involves a polymerizationbetween a preformed polymer and the flame retardant reagent, one mayconceive to incorporate crosslinking activators which will furtherenhance the efficiency of the crosslinking reaction.

It is usual to incorporate a crosslinking/grafting initiator e.g.organic peroxide, which enhances the above reaction. In the case ofcrosslinking, a coagent multifunctional crosslinking e.g. triallylcyanurate may be used to improve efficiency and crosslinking density."

In discussing Table 3 at page 6 line 64 et seq. it is stated that:

". . . the flame retardant reagents used according to the presentinvention, result in a very high degree of crosslinking as shown by thegel content."

Amongst coagents suggested for crosslinking are bisazodicarboxylates,diallyl phthalate, triallyl cyanurate, triallyl isocyanurate,divinylbenzene, S₂ Cl₂, dimaleimides, ethylene dimethacrylate, ethyleneglycol dimethacrylate, and 1,3-butylene glycol dimethacrylate. Typicalprocessing conditions include blending masterbatches, elastomer andcomponents (except dicumyl peroxide) in the plasticorder at 125° C. for20 minutes at 20-25 r.p.m. followed by introduction of the peroxide andmixing it into the polymer for 3 minutes. The molten mass was removedfrom the mixing cell, transferred to a press and cured into a plate 2 mmthick for 30-45 minutes at 130° C.

EP-A-0044233 to Societe Chimique des Charbonnages S.A. describes aprocess in which styrene is polymerised in the presence of a rubberyterpolymer of ethylene, propylene and a third component, such asethylidene norbornene, in the presence of a peroxide characterised inthat the rubbery solution of monomers is polymerised in the mass in thepresence of a monomer selected from divinylbenzene, triallyl cyanurateand glycol acrylate. The resultant product is cross-linked since it hasa significant gel content.

Production of cross-linked polypropylene is described in JP-A-58/67446to Tokuyama Soda K.K. According to this proposal a polymer which ispolypropylene, a propylene/ethylene block or random copolymer, apropylene/α-olefin copolymer or a mixture thereof is blended with anunsaturated carboxylic acid such as maleic anhydride, a crosslinkingaid, such as divinylbenzene, divinyltoluene, diallyl glycerate or liquidrubber comprising a diene monomer, and an organic peroxide, and theresulting blend is hot pressed against a metal product at more than themelting point of the polymer and then heated to a temperature higherthan the decomposition point of the organic peroxide to crosslink thepolymer.

Graft copolymers for use as ion exchange fibres are described inJP-A-53/8693 and JP-A-53/8694 to Japan Atomic Energy Research; in theformer specification polyamides and in the latter specificationpolyesters undergo graft polymerisation with hydroxystyrenes and/oracyloxystyrenes, preferably in the presence of polyene compounds, suchas divinylbenzene, using ionising radiation.

Although many attempts have been made to produce non-extractableantioxidants and stabilisers by polymerising, copolymerising orgrafting-of antioxidants containing polymerisable vinyl groups, fewcommercial products are available in spite of the substantial activityin the patent literature. The literature has been reviewed in"Developments in Polymer Stabilisation -4" (Ed: G. Scott) 1981, page181, and, ACS Symposium. Series 280. 173 (1985).

The reasons for the lack of commercial success of the prior art areessentially:

(i) Homopolymerised antioxidants are incompatible with other polymersand consequently have low antioxidant activity.

(ii) Copolymers of vinyl antioxidants and normal monomers, althoughoxidatively stable, are much more expensive to manufacture thanconventional large tonnage plastics such as polyethylene, polypropylene,polyvinyl chloride and polystyrene since the scale of manufacture ismuch reduced. No new oxidatively stable plastics based on these monomersare believed to be in commercial production.

(iii) Grafting of vinyl antioxidants and stabilisers on to preformedpolymers has been widely reported but, again, no commercial productshave been produced since the efficiency of the binding process isgenerally low and the products so produced are not sufficientlyeffective to justify the cost of the modification procedure.

The cost of modifying all the polymer substrate can in principle beavoided by carrying out the antioxidant grafting process in such a wayas to produce a concentrated masterbatch of bound antioxidant which cansubsequently be used as a normal additive for polymers duringprocessing. This procedure has been used previously for thiol adducts tothe double bond in rubbers, but is much more difficult to carry out onsaturated polymers due to the inefficiency of the grafting processreferred to above.

An object of the present invention is to obviate or mitigate theaforesaid disadvantages. In particular the invention seeks to provide amethod of making graft copolymers in which the amount of residualmonomeric material left in the resulting graft copolymer is reduced to avery low content and under favourable circumstances substantially tozero or near zero. It further seeks to provide graft copolymerscontaining functional groups in which the degree of binding of themonomer containing the functional groups is enhanced compared with priorart methods.

According to the present invention there is provided a modified polymercapable of being blended as a masterbatch with an unmodified polymer.This modified polymer is comprises of a thermoplastic polymercomposition comprising a graft copolymer between (1) a preformedthermoplastic polymer and (2) a two component monomer compositioncontaining (a) at least one polymerizable monomer containing anethylenically unsaturated polymerizable group and at least onefunctional polymer-modifying group and (b) at least one comonomercontaining at least two ethylenically unsaturated polymerizable groups.The preformed thermoplastic polymer (1) and the monomer composition (2)contained in the modified polymer are used in proportions such as toform a masterbatch concentrate for blending with unmodified polymer. Theresulting graft copolymer has a gel content of less than 0.5% by weightand is substantially free of unbound monomer. By the term "substantiallyfree of unbound monomer," we mean that less than 10% of the startingmonomer remains in the graft copolymer and can be removed by physicalseparation processes.

The present invention also provides a method of preparing a modifiedpolymer capable of being blended as a masterbatch with an unmodifiedpolymer by reacting together at a temperature of from 70° C. to 300° C.in a melt and in the presence of free radicals while applying shear tothe melt, a preformed thermoplastic polymer to be modified and a twocomponent monomer composition containing (a) at least one polymerizablemonomer having ethylenically unsaturated polymerizable group and atleast one function polymer-modifying group and (b) at least onecomonomer containing no functional polymer-modifying group but at leasttwo ethylenically unsaturated polymerizable groups. This grafts thepolymerizable monomer or monomers to the preformed polymer leavingsubstantially no unbound monomer. The reaction is continued for a periodof time such that the torque used in applying shear to the melt passesthrough a peak and then falls again, and this produces a graft copolymerthat is thermoplastic with a gel content of less than 0.5% by weight andthat can be blended with an unmodified polymer.

The graft copolymer composition is thus typically formed from threecomponents, i.e. a preformed thermoplastic polymer (sometimeshereinafter called the unmodified polymer), a ethylenically unsaturatedpolymerisable monomer containing a ethylenically unsaturatedpolymerisable group and one or more functional polymer-modifying groups,and a comonomer that contains two or more, e.g. 3, ethylenicallyunsaturated polymerisable groups.

Preferably the preformed thermoplastic polymer (1) and the monomercomposition (2) are used in proportions such as to form a masterbatchconcentrate for addition to unmodified polymer.

Hence the invention also relates to polymer blends comprising anunmodified thermoplastic polymer and a modified polymer according to theinvention.

The monomer composition may be a mixture of (a) at least one monomerpossessing a functional group and a single ethylenically unsaturatedpolymerisable group and (b) at least one comonomer having at least twoethylenically unsaturated polymerisable groups with or without afunctional polymer-modifying group. Usually the comonomer has nofunctional polymer-modifying group.

The comonomer (a) or, if more than one comonomer (a) is used, eachcomonomer (a) contains usually one ethylenically unsaturatedpolymerisable group, and the or each comonomer (b) contains usually twoor three ethylenically unsaturated polymerisable groups. Suchpolymerisable groups, which may be the same or different in the monomer(a) and in the comonomer (b), are usually polymer reactive vinyl groupsand may be selected from, for example, acryloyl, methacryloyl, allyl,vinyl- or allyl- substituted aromatic, heterocyclic, or cycloaliphaticgroups, and vinyl or allyl ester groups. If desired, the or eachcomonomer (b) may contain two or more different ethylenicallyunsaturated polymerisable groups.

By the term "functional polymer-modifying group", or "functional group",is intended a group which imparts physical or chemical activity to amolecule and examples of such which may be utilised in the presentinvention are carboxyl, ester, amine, amide, acyl, anhydride, thiol andsilane groups. Particular examples of suitable materials are; groupswhich modify the ageing behaviour of the polymer such as, chain-breakingantioxidants (notably hindered phenols, hindered aliphatic amines andaromatic amines); peroxide decomposing antioxidants such as sulphides,dithiocarbamates, xanthates, dithiophosphates, mercaptobenzothiazoles,mercaptobenzimidazoles, phosphites and cyclic phosphate esters;photosensitisers such as transition metal compounds, particularly irondithiocarbamates; UV absorbers such as, 2-hydroxybenzophenones and2-hydroxybenzothiazoles; and, metal deactivating agents such as ethylenediamine tetraacetic acid, disalicylidine ethylene diamines andbis-hydrazides. Another class of suitable materials contains groupswhich modify the physical behaviour of the polymer such as, polar groupsattached to non-polar polymers to give increased--adhesion to inorganicsubstrates, for example, NO₂, Cl, CN, SO₃ H, and R₄ N⁺, or, non-polargroups attached to polar polymers such as PVC to give a plasticisingeffect.

The said monomer composition may, therefore, comprise (i) at least onemonomer having molecules containing one or more desired functionalgroups and which also contain one ethylenically unsaturatedpolymerisable group capable of being attached to the polymer and (ii) atleast one co-reactant in the form of a comonomer whose molecules neednot possess the desired functionality but which have at least twoethylenically unsaturated polymerisable groups capable of being attachedto the polymer.

It is known in polymer technology that monomers containing two or morepolymerisable groups, such as vinyl or allyl groups, very often act ascross-linking agents upon introduction into polymers by copolymerisationor by graft polymerisation. Examples of such teachings in the prior artinclude the above mentioned EP-A-0247861, EP-A-0044233, JP-A-58/67446,JP-A-53/8693 and JP-A-53/8694. Moreover it is recognised that the morepolymerisable groups that are present in a monomer, the greater is thetendency to introduce cross-linking into the molecules of a graftpolymer or of a copolymer. Hence, in general, a monomer containing threeor more polymerisable groups is a better cross-linking agent than asimilar monomer having only two such groups. Such cross-linking isusually accompanied by a corresponding increase in rigidity of theresulting copolymer or graft polymer, with the result that a graftpolymer formed by modifying a thermoplastic polymer using a comonomerwith two, three or more polymerisable groups may prove to be toointractable to permit blending with an unmodified polymer, such as theunmodified polymer from which the graft polymer is prepared.

It is accordingly very surprising that, although the comonomer containstwo or more ethylenically unsaturated polymerisable groups and hencewould be expected to introduce cross-linking into the graft polymermolecule and to render it too intractable to permit blending intounmodified polymer, yet using the teaching of the present invention itis possible to produce graft polymers which are of similar molecularweight to the original polymer and which are still thermoplastic so thatthey can be blended with unmodified polymers as though they contained nomodifying groups in substantially any proportion, for example in aweight ratio of from about 100:1 to about 1:100. Hence the inventionprovides a considerable advance in making polymeric additives which canbe used as additives for introducing desired properties into polymercompositions.

It is further surprising that the invention can be practised usingpolymers, such as polypropylene, which normally tend to undergodepolymerisation at high temperatures in the presence of free radicals,and that the resulting modified polymer does not suffer a significantreduction in molecular weight.

The invention also provides a method of preparing the modifiedthermoplastic polymers aforesaid comprising reacting together, in a meltand in the presence of free radicals whilst applying shear to the melt,a preformed thermoplastic polymer to be modified and a two componentmonomer composition comprising (a) at least one polymerisable monomercontaining a ethylenically unsaturated polymerisable group and at leastone functional polymer-modifying group and (b) at least one comonomercontaining at least two ethylenically unsaturated polymerisable groups,thereby to graft said monomer to said preformed polymer leavingsubstantially no unbound monomer, the reaction being continued for aperiod of time sufficient to produce a graft copolymer that isthermoplastic and can be blended with an unmodified polymer.

This reaction is preferably conducted in the absence of free molecularoxygen.

This principle, although applicable to antioxidants and stabilisers, isalso more broadly applicable to any kind of modifying agent for polymersincluding agents whose function is to improve adhesion of the polymer toinorganic materials (such as metals, glass, fibres and fillers), agentsto plasticise or to cross-link the polymer, to modify the electrical orthermal conductivity of the polymer, to modify dyeability, to modify thesurface properties (for example hydrophilicity or antistatic behaviour),agents to impart particular chemical reactivity to the polymer so thatit can be reacted with other polymers or with similarly modifiedpolymers to give block or graft copolymers which can be used as solidphase dispersants in polymer blends (so-called "compatibilisers") andagents which photosensitise the photo-oxidation of polymers. This listis not intended to be exhaustive since the process of the invention isapplicable to any polymer modification reaction where, ideally, no lowmolecular weight modifier or oligomer remains in the polymer afterreaction. That is, the modifying agent becomes an integral part of thepolymer as a result of reaction of its polymerisable group and cannot beremoved by physical separation processes.

The invention is based on the discovery that polymer modifying moleculescan be grafted to polymers, using melt reaction conditions and withapplication of mechanical shear, in the presence of free radicals,leaving few or none of the modifier molecules in the free state in whichthey could subsequently leach from the polymer in use. To enable this tobe effected, it is necessary to introduce a polymer-reactive group intothe modifier molecule in addition to the structures which impart themodifying property. In total there have to be at least threeethylenically unsaturated polymerisable groups in the monomercomposition and this may be achieved by providing two (or more) suchgroups in the comonomer and one such polymerisable group on the modifiermolecule provided that the comonomer need not have any modifyingproperties so long as it contains two or more ethylenically unsaturatedpolymerisable groups.

The graft polymerisation reaction may be conducted in the presence of afree radical generator such as an organic peroxide or an azo compound.Alternatively the graft polymerisation reaction can be carried out inthe presence of free radicals produced solely by the shearing of thepolymer, for example in an extruder or high shear mixer. Ultrasound orultraviolet irradiation or by any high energy radiation, such asionising radiation from a nuclear reactor or from a radioactive source,can be used to generate free radicals.

The polymer is modified by use of a two component monomer compositioncontaining a minimum of two components, for example: ##STR1## where X isethylenically unsaturated polymerisable group, Y is a group or a mixtureof groups possessing the desired modifying functionality, and R and R'which may be the same or different are alkyl, aralkyl or othersubstituents. Throughout this specification any alkyl groups, oralkylene group forming, for example, part of an aralkyl group, containspreferably from 1 to 6 carbon atoms and even more preferably 1 to 4carbon atoms.

The invention provides a particularly convenient way of incorporatingmore than one modifying molecule into a polymer bound masterbatchfunctional compound provided the modifying molecules are copolymerisablewith the comonomer which contains more than one polymerisable group,e.g. mixtures of modifying molecules of the formulae:

    CH.sub.2 =CHCOOY and CH.sub.2 =CHCOOZ,

where Y and Z represent different functional polymer-modifying groups.

This is particularly valuable in antioxidant/modifier technology wheresynergistic combinations of bound antioxidants are frequently required.

The modifying groups represented by Y and Z may be any desiredfunctional groups, and may typically contain antioxidants, UV absorbers,dyeing modifiers, cross-linkable groups, coupling agents, groups topromote adhesion, reactive groups to which to attach a second polymerchain, plasticiser groups and the like.

Examples of polymerisable monomers are as follows: ##STR2## where Xrepresents O, NH, or S; ##STR3## where n is zero or an integer from 1 to10, and X is O, NH or S; ##STR4## where n is an integer from 1 to 16,and X is O, NH or S; ##STR5## where R is hydrogen or an alkyl or aralkylgroup, R' is an alkyl or aralkyl group and X⁻ is a polymer compatibleanion, such as a chloride anion.

Examples of comonomers include the following: ##STR6## where R is asdefined above; R" is an aliphatic, heteroaliphatic, cycloaliphatic,aromatic, or heterocyclic group; n is an integer of at least 2,preferably an integer in the range of from 2 to 6; X is a divalentradical which may include one or more linking groups such as --CO--O--,--CO--NH--, --O--, --S--, --NR₁ --, and --CR₁ R₂ --; R₁ and R₂ are eacha hydrogen atom or a hydrocarbon radical, such as an alkyl radical; andp is zero or 1.

Representative examples of comonomers which may be used are: ##STR7##where R is a hydrogen, alkyl or aralkyl group.

In formulae (viii), (ix) and (xi) the second indicated group can be inthe o-, m-, or p- position. In formula (×) the three groups can be inany permissible positions relative to one another.

Specific examples of comonomers which can be used in the practice of thepresent invention include trisacryloyl trimethylol propane (TMPTA) ofthe formula: ##STR8## tris-acryloyl trimethylol butane (TMBTA) of theformula: ##STR9## divinyl benzene (DVB), and triallyl cyanurate (TAC).

Preferred examples of polymerisable monomers containing a functionalgroup and at least one functional polymer-modifying group include2-hydroxy-4-(β-acryloyloxyethoxy)-benzophenone (HAEB),4-acryloyloxy-2,2,6,6-tetramethyl piperidine (AOTP), tetraethylenepentamine monoacrylate (TEPAA), vinyl trimethoxysilane (TMVS),β-acryloyloxyethyl trimethoxy silane (AETS), 4-vinylbenzoic acid (VBA),2,6-di-t-butyl-4-hydroxybenzyl acrylate (DBHBA), and2-(2'-hydroxy-5'-vinylphenyl) benzotriazole (HVPB).

Compounds which can be added as free radical generators include dicumylperoxide (DCP), 2,5-bis-t-butylperoxy-2,5-dimethylhexane (otherwisecalled 2,5-dimethyl- 2,5-t-butyl-peroxy-hexane (BPH)), di-t-butylperoxide (DTBP), and di-t-butyl peroxy carbonate (DTBPDC).

As examples of thermoplastic polymers which can be used in the inventionas the starting polymer there can be mentioned, for example, vinylpolymers and copolymers and substantially linear condensation polymers.The invention can thus be used to modify vinyl polymers and copolymersincluding, for example, polyolefins, such as polyethylene andpolypropylene, polyvinyl chloride, polystyrene, ethylene-propylene co-and ter-polymers, polyacrylates, polymethacrylates, polyacrylonitrile,and acrylonitrile-butadiene-styrene terpolymers. Examples ofthermoplastic condensation polymers which can be utilised in thepractice of this invention include polyamides, such as nylon-6,nylon-66, nylon 610, and the like, linear polyesters, such aspolyethylene terephthalate and polybutylene terephthalate, and the like,and linear and substantially linear polyurethanes.

Although the reaction mechanism has not been fully explored the resultsobserved are consistent with the following explanation, the correctnessor otherwise of which is not intended to affect the validity of thepresent application. In the melt free radicals are generated by theshearing forces applied which cause cleavage of the polymer chains andalso as a result of decomposition of any free radical generator that maybe added or as a result of any external influence, such as ionisingradiation. Such free radicals can in turn strip hydrogen atoms off thepolymer molecule to form corresponding free radicals on the polymerchain, with which the ethylenically unsaturated polymerisable groups onthe monomer (a) or the comonomer (b) can then react to form side chainsand even crosslink the polymer chains. At least the majority of suchside chains and cross-linkages are then broken under the influence ofthe continued shearing to yield a modified polymer, typically withapproximately the same molecular weight as the starting polymer, whichis still thermoplastic and is compatible with unmodified polymer.However, in some cases, an increase in molecular weight can be observedand may not be disadvantageous.

Typical reaction conditions include, besides exclusion of free molecularoxygen, use of a temperature above the melting point of thethermoplastic polymer and higher than the decomposition temperature ofthe free radical generator, if used, and shear conditions sufficient toblend the components of the reaction melt but not such as to causesignificant degradation of the unmodified polymer in the absence of theother components. Such reaction conditions may thus include use of atemperature of at least about 70° C., for example a temperature in therange of from about 130° C. to up to about 400° C. The precisetemperature to be used in part by the melting point of the polymer andby its stability. In any event the temperature used should not be sohigh as to cause significant degradation of the polymer. Normally itwill be preferred to use a temperature of not more than about 300° C.,preferably in the range of from about 150° C. to about 230° C. If a freeradical generator is used it should be selected so that itsdecomposition temperature is above the melting point of the melt, andpreferably above the melting point of the unmodified polymer.

As will be appreciated, the lower the melting point of the unmodifiedpolymer is, the lower is the temperature that can be contemplated foruse in the method of the invention. Similarly, if an unmodified polymerof low melting point is selected, then the use of a free radicalgenerator with a correspondingly low decomposition temperature can becontemplated. For example, when using an ethylene-propylene rubber inthe method of the invention the use of a peroxydicarbonate, such asdi-t-butyl peroxydicarbonate which has a decomposition point of about100° C., can be contemplated. The precise reaction conditions to be usedwill thus depend upon the particular unmodified polymer selected andupon the free radical generator (if any) used, as well as upon theamounts of polymerisable monomer and comonomer that may be used, whichwill in turn affect the temperature at which a satisfactory melt isformed. The man skilled in the art will readily be able to find suitablereaction conditions for a given unmodified theremoplastic polymer by aprocess of trial and error, if necessary.

The reaction time will depend upon such factors as the type of polymerbeing treated, the reactivity of the at least one polymerisable monomer(a) and of the at least one commonomer (b), the decompositiontemperature of any free radical generator added, and above all upon thetype of equipment used to carry out the method of the invention, inparticular upon its efficiency in heating, mixing and applying shear tothe ingredients of the melt. It is typically at least about 2 minutes upto about 30 minutes. Normally it will be preferred to use a reactiontime of less than about 20 minutes. In many cases it will suffice to usea reaction time of about 5 minutes up to about 15 minutes, for examplewhen using polypropylene as the starting polymer. However, it ispreferred to use as short a reaction time as possible, consistent withobtaining a graft copolymer that is thermoplastic and can be blendedwith unmodified polymer, so as to avoid significant degradation of thepolymer.

The method of the invention can be operated batchwise using, forexample, a Banbury mixer or other internal mixer. It may also be carriedout in a continuous manner using a high shear mixer, such as a Busskokneader or a twin screw extruder.

The progress of the reaction can be monitored in performance of a batchreaction by measuring the torque required to operate the mixer. It isfound that this torque measurement initially increases, passes through apeak, and then falls, possibly back to a value substantially the same asthat required to operate the mixer with a charge of the unmodifiedpolymer and with no added monomer composition. The reaction is normallycontinued at least until the torque peak has passed.

Another way of monitoring the progress of the method of the invention isto measure the gel content of the resulting graft copolymer. Aconvenient way of measuring the gel content is to test the solubility ofthe graft copolymer in a suitable solvent. For example, when usingpolypropylene as the starting polymer, p-xylene is a suitable solvent. Amethod for measuring the gel content is described, for example in ASTMD-638-68. When the gel content has reduced substantially to zero, e.g.to about 0.5 percent by weight or less and preferably to about 0.1% byweight or less, then the graft copolymer will be thermoplastic and canbe blended with modified polymer.

The molecular weight of the graft is typically approximately the same asthe modified starting polymer or somewhat higher.

The invention will now be described, by way of illustration, by thefollowing Examples. In each of Examples 1 to 4 and 6 to 8 an increase inmelt viscosity was initially observed in the course of the reaction butupon continuing the reaction the melt viscosity dropped backsubstantially to its original value.

EXAMPLE 1

A mixture of unmodified polypropylene and2-hydroxy-4-(β-acryloyloxyethoxy)-benzophenone (HAEB) in a weight ratio90:10, was processed in an internal mixer at 180° C. with the additionof tris-acryloyl trimethylolpropane (TMPTA) and dicumyl peroxide (DCP).The molar ratio of TMPTA to HAEB was 0.1:1 and the molar ratio of DCP toTMPTA was 0.002:1. The reaction time was 15 minutes. The product wascompression moulded to film and the amount of the UV absorber (HAEB)remaining after extraction with methylene dichloride was estimated by UVspectroscopy. This was found to be 100% of the amount incorporatedduring processing and no HAEB could be detected in the extractingsolvent.

EXAMPLE 2

Example 1 was repeated but dicumyl peroxide was replaced by2,5-bis-t-butylperoxy-2,5-dimethylhexane (BPH) (Trade Mark Triganox 101)at a BPH:TMPTA molar ratio of 0.0025:1. The results on testing were thesame as reported in Example 1.

EXAMPLE 3

Example 1 was repeated except that the HAEB was replaced by4-acryloyloxy-2,2,6,6-tetramethyl piperidine (AOTP). After extraction,the films were found to contain all the original AOTP incorporated intothe mix and none could be detected in the solvent.

EXAMPLE 4

Example 2 was repeated with replacement of the HAEB with AOTP. The sameresult as reported in the previous Examples was obtained.

EXAMPLE 5

Four grams of the product of Example 4 were mixed with 96 grams ofunstabilised polypropylene in an internal mixer for 5 minutes at 180° C.Films were made by compression moulding of the polymer at 180° C. andwere then extracted for 48 hours with methanol under reflux. The filmswere exposed to UV light in an accelerated weathering cabinet (sunlamp/actinic blue lamp) and were found to embrittle after 1800 hours. Aconventional HALS (Tinuvin 770), incorporated into polypropylene at thesame functional group concentration (0.4 g/100 g) was found to embrittleat 1500 hours before methanol extraction and at 130 hours followingmethanol extraction.

EXAMPLE 6

The mixing procedure of Example 5 is repeated with the modified polymerof Example 2 to give a blend with similar properties to that of Example5.

EXAMPLE 7

Using a similar blending procedure to that described in Example 5 themodified polymer of Example 3 is admixed with an unmodifiedpolypropylene. Compared with the unmodified polymer the blend shows goodu.v. stability and resistance to oxidation.

EXAMPLE 8

When the procedure of Example 7 is repeated with the product of Example4 similar results are obtained.

EXAMPLE 9

A mixture of unmodified polypropylene and tetraethylene pentaminemonoacrylate (TEPAA) in a weight ratio of 95:5 was processed in aninternal mixer at 180° C. with the addition of trimethylol propanetriacrylate (TMPTA) and 2,5-dimethyl-2,5-t-butyl-peroxy-hexane (BPH).The molar ratio of TMPTA to TEPAA was 0.2:1 and the molar ratio of BPHto TMPTA was 0.0003:1. The reaction time was 10 minutes. The product wascompression moulded to film and the amount of TEPAA remaining afterextraction with dichloromethane was estimated by spectrophotometry. Thiswas found to be 90% of the amount present before extraction.

EXAMPLE 10

A mixture of unmodified polypropylene and vinyl trimethoxysilane (TMVS)in a weight ratio of 90:10 was processed in an internal mixer at 180° C.with the addition of trimethylol propane triacrylate (TMPTA) and2,5-dimethyl-2,5-t-butyl-peroxy-hexane (BPH). The molar ratio of TMPTAto TMVS was 0.1:1 and the molar ratio of BPH to TMPTA was 0.001:1. Thereaction time was 10 minutes. The masterbatch product was compressionmoulded to film and the amount of TMVS remaining after extraction withdichloromethane was estimated by spectrophotometry. This was found to be95% of the amount present before extraction. Silane linkages in theproduct are capable of being cross-linked by treatment with water.

EXAMPLE 11

A mixture of unmodified polypropylene and 4-vinylbenzoic acid (VBA) in aweight ratio of 99:1 was processed in an internal mixer at 180° C. withthe addition of trimethylol propane triacrylate (TMPTA) and2,5-dimethyl-2,5-t-butyl-peroxy-hexane (BPH). The molar ratio of TMPTAto VBA was 0.1:1 and the molar ratio of BPA to TMPTA was 0.0015:1. Thereaction time was 10 minutes. The product was compression moulded tofilm and the amount of VBA remaining after extraction withdichloromethane was estimated by spectrophotometry. This was found to be99% of the amount present before extraction.

EXAMPLE 12

The product of Example 9 is found to be compatible with polypropyleneand to enable large amounts of alumina trihydrate to be blendedtherewith for the purpose of imparting flame retardant properties to theblend.

EXAMPLE 13

The product of Example 10 is compatible with unmodified polypropyleneand the resulting blend can be admixed with glass fibres to give asatisfactory reinforced polymer product.

EXAMPLE 14

The product of Example 11 is found to be compatible with unmodifiedpolypropylene. The resulting blend upon mixing with zinc oxide yields asatisfactorily cross-linked product. It also exhibits satisfactoryantistatic properties and water wettability.

EXAMPLE 15

Following the general procedure of Examples 1 to 4, and 9 to 11 anethylene-propylene rubber in admixture with β-acryloyloxyethyltrimethoxysilane (AETS) in a weight ratio of 90:10 is processed at 100°C. in an internal mixer with the addition of trimethylol propanetriacrylate (TMPTA) and di-t-butyl peroxydicarbonate (DBPDC) until thetorque passes through a peak and falls again. The molar ratio of TMPTAto AETS is 0.1:1 and the molar ratio of DBPDC to TMPTA is 0.001:1. Theproduct is compression moulded and the incorporation of AETS is found tobe efficient. It is readily dispersed in the unmodified rubber.

EXAMPLE 16

The procedure of Example 10 is repeated using, in place of vinyltrimethoxysilane (TMVS), an equivalent amount ofβ-acryloxyethyltrimethoxy silane. A similar product is obtained which isreadily dispersed in unmodified polypropylene.

EXAMPLE 17

The procedure of Example 16 is repeated with polyethylene, polyethyleneterephthalate, and nylon 6. The resulting graft copolymers can beblended with the corresponding unmodified polymer in each case withsimilar results.

EXAMPLE 18

A mixture of 90 parts by weight of unmodified polypropylene and 10 partsby weight of a mixture of 4-acryloyloxy-2,2,6,6-tetramethyl piperidine(AOTP) and trisacryloyl trimethylol propane (TMPTA) was processed in aninternal mixer at 180° C. with the addition of2,5-bis-t-butylperoxy-2,5-dimethylhexane (BPH). The weight ratio ofTMPTA to AOTP was 20:80 and the molar ratio of BPM to the mixture ofTMPTA and AOTP was 0.005:1. The reaction time was 10 minutes.

2.5 grams of the product were mixed with 95.3 grams of unstabilisedpolypropylene and with 0.2 g of "Cyasorb UV-531" (Trade Mark) in aninternal mixer for 10 minutes at 180° C. Films were made by compressionmoulding of the thus treated polymer at 180° C.

Samples of film made in this way were exposed to UV light in anaccelerated weathering cabinet (sun lamp/actisic blue lamp) and werefound to embrittle after 3000 hours.

These results demonstrate a very high synergistic effect.

EXAMPLE 19

A mixture of unmodified polypropylene and acrylic acid (AA) in a weightratio of 97.5:2.5 was processed in an internal mixer at 180° C. with theaddition of trimethylol propane triacrylate (TMPTA) and2,5-dimethyl-2,5-t-butyl peroxy hexane (BPH). The molar ratio of TMPTAto AA was 0.25:1 and the molar ratio of BPH to TMPTA was 0.0035:1. Thereaction time was 10 minutes. The product was compression moulded tofilm and the amount of AA remaining after extraction withdichloromethane was estimated by spectrophotometry. This was found to be92% of the amount present before extraction.

EXAMPLE 20

A mixture of unmodified polypropylene and acrylic acid (AA) in a weightratio of 97.5:2.5 was processed in an internal mixer at 180° C. with theaddition of triallyl cyanurate (or 2,4,6-triallyloxy-1,3,5-triazine)(TAC) and 2,5-dimethyl-2,5-t-butyl peroxy hexane (BPH). The molar ratioof TAC to AA was 0.30:1 and the molar ratio of BPH to TAC was 0.003:1.The reaction time was 10 minutes. The product was compression moulded tofilm and the amount of AA remaining after extraction withdichloromethane was estimated by spectrophotometry. This was found to be95% of the amount present before extraction.

EXAMPLE 21

A mixture of unmodified polypropylene and 2,6-di-tert-butyl-4-acryloxylbenzyl phenol (DTBABP) in a weight ratio of 97:3 was processed in aninternal mixer at 180° C. with the addition of Divinyl benzene (DVB) and2,5-dimethyl-2,5-t-butyl peroxy hexane (BPH). The molar ratio of DVB toDTBABP was 1.5:1 and the molar ratio of BPH to DVB was 0.05:1. Thereaction time was 10 minutes. The product was compression moulded tofilm and the amount of DTBABP remaining after extraction withdichloromethane was estimated by spectrophotometry. This was found to be90% of the amount present before extraction.

EXAMPLE 22

Upon repeating the procedure of Example 7 with the modified polymers ofExamples 19, 20 and 21 satisfactory blending with unmodifiedpolypropylene is observed.

We claim:
 1. A method of preparing a modified polymer capable of beingblended as a masterbatch with an unmodified polymer comprising reactingtogether at a temperature of from 70° C. to 300° C. in a melt and in thepresence of free radicals while applying shear to the melt, a preformedthermoplastic polymer to be modified and a two component monomercomposition comprising (a) at least one polymerizable monomer containingan ethylenically unsaturated polymerizable group and at least onefunctional polymer-modifying group and (b) at least one comonomercontaining no functional polymer-modifying group but at least twoethylenically unsaturated polymerizable groups, thereby to graft saidpolymerizable monomer to said preformed polymer leaving substantially nounbound monomer, the reaction being continued for a period of time suchthat the torque used in applying shear to the melt passes through a peakand then falls again, thereby to produce a graft copolymer that isthermoplastic with a gel content of less than 0.5% by weight and thatcan be blended with an unmodified polymer.
 2. A method according toclaim 1, in which the preformed thermoplastic polymer is a vinyl polymeror a linear condensation polymer.
 3. A method according to claim 1, inwhich the polymerisable monomer is selected from the group consisting of2-hydroxy-4-(β-acryloyloxyethoxy)-benzophenone (HAEB),4-acryloyloxy-2,2,6,6-tetramethyl piperidine (AOTP), tetraethylenepentamine monoacrylate (TEPAA), vinyl trimethoxysilane (TMVS),β-acryloyloxyethyl trimethoxy silane (AETS), 4-vinylbenzoic acid (VBA),2,6-di-t-butyl-4-hydroxybenzyl acrylate (DBHBA), and2-(2'-hydroxy-5'-vinylphenyl)-benzotriazole (HVPB).
 4. A methodaccording to claim 1, in which the polymerisable monomer is selectedfrom the group consisting of compounds of the following formulae:##STR10## where X represents O, NH, or S; ##STR11## where n is zero oran integer from 1 to 10, and X is O, NH or S; ##STR12## where n is aninteger from 1 to 16, and X is O, NH or S; ##STR13## where R is hydrogenor an alkyl or aralkyl group, R' is an alkyl or aralkyl group and X⁻ isa polymer compatible anion.
 5. A method according to claim 1, in whichthe comonomer is selected from the group consisting of compounds of thefollowing formulae: ##STR14## where R is a hydrogen, alkyl or aralkylgroup.
 6. A method according to any one of claim 1, in which thecomonomer is selected from the group consisting of tris-acryloyltrimethylol propane (TMPTA) of the formula: ##STR15## divinylbenzene(DVB), and triallyl cyanurate (TAC).
 7. A method according to claim 1 inwhich the weight ratio of the monomer composition to the preformedthermoplastic polymer is from about 0.001:1 to about 2:1.
 8. A methodaccording to claim 1 in which the weight ratio of the monomercomposition to the preformed thermoplastic polymer is from about 0.05:1to about 1:1.
 9. A method according to claim 1, in which the molar ratioof the comonomer to the polymerisable monomer is from about 0.05:1 toabout 1:1.
 10. A method according to claim 9, in which the molar ratioof the comonomer to the polymerisable monomer is from about 0.1:1 toabout 0.5:1.
 11. A method according to claim 1, in which the reaction isconducted in the presence of an added free radical generator.
 12. Amethod according to claim 11, in which the added free radical generatoris selected from dicumyl peroxide (DCP),2,5-bis-t-butylperoxy-2,5-dimethylhexane (BPH), di-t-butyl peroxide(DTBP), and di-t-butyl peroxydicarbonate.
 13. A method according toclaim 11, in which there is added a free radical generator in a molarratio of the free radical generator to the polymerisable monomer of fromabout 0.00005:1 to about 0.1:1.
 14. A method according to claim 13, inwhich there is added a free radical generator in a molar ratio of thefree radical to the polymerisable monomer of from about 0.0001:1 toabout 0.02:1.
 15. A method according to claim 1, in which the preformedthermoplastic polymer and the monomer composition are used inproportions such as to form a masterbatch concentrate for blending withunmodified polymer.
 16. A method according to claim 1, in which the atleast one functional polymer-modifying group in the polymerisablemonomer (a) comprises a silicon-containing group.
 17. A method accordingto claim 1, in which the silicon-containing group is of the formula--Si(OR')₃ ; where R' is an alkyl group of 1 to 4 carbon atoms.
 18. Amethod according to claim 16, in which the graft polymer is subsequentlysubjected to cross-linking conditions whereby the silicon-containinggroups present in the modified polymer from the polymerisable monomer(a) undergo cross-linking to form a cross-linked polymer.
 19. Across-linked polymer made by a method according to claim
 18. 20. Amodified polymer produced by a method according to claim
 1. 21. A blendof a modified polymer according to claim 20 with an unmodified polymer.22. Articles made from, or comprising, modified polymer according toclaim
 20. 23. A modified polymer capable of being blended as amasterbatch with an unmodified polymer, said modified polymer comprisinga thermoplastic polymer composition comprising a graft copolymer between(1) a preformed thermoplastic polymer and (2) a two component monomercomposition comprising (a) at least one polymerizable monomer containingan ethylenically unsaturated polymerizable group and at least onefunctional polymer-modifying group and (b) at least one comonomercontaining at least two ethylenically unsaturated polymerizable groups,said preformed thermoplastic polymer and the monomer composition beingin proportions such as to form a masterbatch concentrate for blendingwith unmodified polymer, and said copolymer having a gel content of lessthan 0.5% by weight and being substantially free of unbound monomer. 24.A modified polymer according to claim 23, in which the preformedthermoplastic polymer is a vinyl polymer, or vinyl copolymer or a linearcondensation polymer.
 25. A modified polymer according to claim 23, inwhich the polymerizable monomer is selected from the group consisting ofcompounds of the following formula: ##STR16## where X represents O, NH,or S; ##STR17## where n is zero or an integer from 1 to 10, end X is O,NH or S; ##STR18## where n is an integer from 1 to 16, and X is O, NH orS; ##STR19## where R is a hydrogen, alkyl or aralkyl group.
 26. Amodified polymer according to claim 23 in which the polymerizablemonomer is selected from the group consisting of2-hydroxy-4-(β-acryloyloxyethoxy)-benzophenone (HAEB),4-acryloyloxy-2,2,6,6-tetramethyl piperidine (AOTP), tetraethylenepentamine monoacrylate (TEPAA), vinyl trimethoxysilane (TMVS),β-acryloyloxyethyl trimethoxy silane (AETS), 4-vinylbenzoic acid (VBA),2,6-di-t butyl-4-hydroxybenzyl acrylate (DBHBA), and2-(2'-hydroxy-5'-vinylphenyl)-benzotriazole (HVPB).
 27. A modifiedpolymer according to claim 23 in which the comonomer is selected fromthe group consisting of compounds of the following formulae: ##STR20##where R is hydrogen or an alky or aralkyl group, t-C₈ H₁₇ is tert-C₈H₁₇, R' is an alkyl or aralkyl group and X₁ is a polymer compatibleanion.
 28. A modified polymer according to claim 23 in which thecomonomer is selected from the group consisting of tris-acryloyltrimethylol propane (TMPTA) of the formula: ##STR21## divinylbenzene(DVB), and triallyl cyanurate (TAC).
 29. A modified polymer according toclaim 23 in which the weight ratio of the monomer composition to thepreformed thermoplastic polymer is from 0.001 to 2:1.
 30. A modifiedpolymer according to claim 29 in which the weight ratio of the monomercomposition to the preformed thermoplastic polymer is from 0.05:1 to1:1.
 31. A modified polymer according to claim 23 in which the molarratio of the comonomer to the polymerizable monomer is from 0.05:1 to1:1.
 32. A modified polymer according to claim 31 in which the molarratio of the comonomer to the polymerizable monomer is from 0.1:1 to0.5:1.
 33. Articles made from or comprising a modified polymer accordingto claim 23.